Method of treating obstructive sleep apnea using electrical nerve stimulation

ABSTRACT

A method for treating a medical condition, such as obstructive sleep apnea, includes the step of stimulating a nerve, particularly the hypoglossal nerve, using at least one of the following techniques: (a) continuous low-level electrical stimulation; (b) electrical stimulation synchronized with a physical process, such as inspiration, without feedback from the nerve being stimulated; and (c) intermittent electrical stimulation at controlled intervals based on the patient&#39;s metabolism.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. Continuation patent application claims priority to and thebenefit of U.S. patent application Ser. No. 11/109,338 filed Apr. 19,2005, which claims priority to and the benefit of U.S. ProvisionalPatent Application Ser. No. 60/667,136 filed on Mar. 31, 2005, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method for treating a medicalcondition using electrical nerve stimulation, and more particularly to amethod for treating obstructive sleep apnea by electrically stimulatingthe hypoglossal nerve.

BACKGROUND

Sleep apnea is characterized by temporary cessation of breathing duringsleep, which can lead to or aggravate many health problems. Obstructivesleep apnea (often abbreviated OSA) is primarily caused by the collapseof the upper airway. The base of the tongue has been found to be acommon site of obstruction in the upper airway, and the upper airwaydilator muscles have been recognized as being important in maintainingan open airway.

Unfortunately, current treatment methods for obstructive sleep apneahave not been consistently effective for all patients. The standardmethod is Continuous Positive Airway Pressure (CPAP) treatment, whichrequires the patient to wear a mask through which air is blown into thenostrils to keep the airway open. Patient compliance is poor due todiscomfort and side effects, such as sneezing, nasal discharge, anddryness. A more recent treatment option, the implantation of rigidinserts in the soft palate to provide structural support, is both moreinvasive and generally is only effective for mild to moderate cases ofobstructive sleep apnea. Alternative treatments are even more invasiveand drastic, including tracheostomy and tissue ablation (somnoplasty oruvulopalatopharyngoplasty (UPPP)). Electrical stimulation of muscles hasbecome another recent treatment option. These treatments have includeddirect electrical stimulation of muscle fibers, as disclosed in U.S.Patent Application Publication No. 2001/0010010 A1, and electricalstimulation of the hypoglossal nerve in a closed-loop system based onfeedback from signals naturally occurring in the hypoglossal nerve, asdisclosed in U.S. Pat. No. 6,456,866 for example.

SUMMARY

The present invention provides a method for treating a medicalcondition, such as obstructive sleep apnea, by directly electricallystimulating a nerve to activate one or more muscles rather thanelectrically stimulating the muscle fibers directly. The method includesstimulating a nerve using at least one of the following techniques: (a)continuous electrical stimulation where a low level of stimulation isprovided to maintain the stiffness of the airway throughout therespiratory cycle; (b) intermittent electrical stimulation initiated inresponse to sensing a physical process, such as inspiration, sensed by aremote sensor without feedback from the nerve being stimulated; or (c)intermittent electrical stimulation at controlled intervals,predetermined based on the patient's resting nighttime metabolism,determined by observing the nighttime respiratory rate, for example.Although other medical conditions might be successfully treated withthis method, this method is well suited for the treatment of obstructivesleep apnea.

Specifically, a method in accordance with the invention includescontrolling the patency of a patient's airway by electricallystimulating a nerve to activate an upper-airway controlling muscle,including intermittently stimulating the nerve at predeterminedintervals based on a patient's metabolism.

Another method in accordance with the invention includes continuouslyelectrically stimulating at least one fascicle of the hypoglossal nerveat a predetermined amplitude of about 10% less than the thresholdamplitude necessary to activate a muscle of a patient up toapproximately the patient's threshold activation amplitude.

Yet another method in accordance with the invention includeselectrically stimulating a nerve and initiating the stimulation inresponse to a physical process other than a signal from the nerve beingstimulated.

Electrically stimulating the nerve requires less power to activate themuscles than stimulating the muscle fibers directly. Stimulating thenerve also activates an entire muscle, rather than simply the musclefibers being stimulated. Direct nerve stimulation also provides theopportunity for directing the stimulation to fascicles of the nerve totune the stimulation for the desired outcome.

Hypoglossal nerve stimulation overcomes the side effects of the CPAPtreatment mentioned above. The mask used for treatment with CPAP is notneeded for hypoglossal nerve stimulation, which also prevents orminimizes problems with skin irritation, claustrophobia and panicattacks. All of these factors facilitate increased patient compliance,while being relatively less invasive than other currently-used surgicalalternatives, and also being more cosmetically appealing. Thus, thisinvention addresses the need to provide a simple but effective method ofstimulating a nerve to treat and/or prevent collapse of the upper airwayduring sleep.

The foregoing and other features of the invention are hereinafter fullydescribed and particularly pointed out in the claims, the followingdescription and annexed drawings setting forth in detail a certainillustrative embodiment of the invention, this embodiment beingindicative, however, of but one of the various ways in which theprinciples of the invention might be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an apparatus and the nerves andmuscles used in treating obstructive sleep apnea.

DETAILED DESCRIPTION

The present invention provides a method for treating a medicalcondition, such as obstructive sleep apnea, by electrically stimulatinga nerve to control one or more muscles to achieve a desired effect for apatient. In the case of obstructive sleep apnea, electrical stimulationof the hypoglossal nerve, for example, can maintain the patency of theupper airway by activating the upper airway dilator muscles, therebyminimizing or eliminating airway collapse during sleep. Electricalstimulation of the lingual nerve also could relieve obstruction byactivating the lingual-hypoglossal reflex loop.

More particularly, a method provided in accordance with the inventionincludes controlling the patency of a patient's airway by stimulating anerve using at least one of the following techniques: (a) continuouslyelectrically stimulating at least one fascicle of the hypoglossal nerveat a predetermined a low level amplitude throughout the respiratorycycle; (b) electrically stimulating a nerve and initiating thestimulation in response to a physical process, such as inspiration,using a remote sensor, without feedback from the nerve being stimulated;and (c) intermittently electrically stimulating a nerve at controlledintervals, predetermined based on the patient's resting nighttimemetabolism, which can be determined from the patient's observedrespiratory rate, for example.

An exemplary apparatus 20 for stimulating a nerve in accordance with thepresent invention is shown schematically in FIG. 1. The apparatus 20includes a control system 22 (shown schematically) for generating thedesired electrical stimulus, and an electrode 24 connected to the nerveto transmit the electrical stimulus to the nerve. The electrode 24preferably is a cuff electrode that provides an intimate connection tothe nerve. The cuff electrode 24 can have a variety of geometries orconfigurations, but preferably provides an intimate connection aroundthe nerve. A lead wire 26 connects the electrode 24 to the controlsystem 22 in the illustrated embodiment.

The control system 22 typically includes a battery, either primary orrechargeable, for powering the apparatus 20. The control system 22 alsotypically includes a processor for setting up stimulation parameters toachieve the desired outcome for the individual patient or otherwisecontrolling the stimulation. By way of example, these parameters caninclude stimulation amplitude, stimulation frequency and stimulationduration. In addition, the control system 22 typically includes amechanism that allows the patient to turn the apparatus 20 on and offand possibly make adjustments within preprogrammed settings.

The control system 22 controls the application of the electricalstimulation based on programmed parameters and can take many forms.Portions of the control system 22, in addition to the electrode 24, canbe implanted in the patient's body. Other portions of the control system22 can be external to the body, and variations can exist betweendifferent control systems. For example, the control system 22 caninclude an implantable pulse generator (IPG) implanted in the body ofthe patient. As another example, in a different embodiment the IPG canbe located within the electrode itself, with information and powersupplied from the controller by light or other electromagnetic means.

The method provided by the invention is not limited by the design of theapparatus used to carry it out. For further information regarding anexemplary apparatus for practicing the method of the invention, refer toU.S. Pat. No. 6,587,725, which is hereby incorporated herein byreference in its entirety.

Although this method can be applied to other medical conditions wherestimulation of a nerve would produce therapeutic or functional outcomesfor a patient's airway, the method described in the following paragraphsfocuses on the treatment of obstructive sleep apnea. In particular, themethod addresses the problem of preventing or treating collapse of theupper airway 28 as a cause of obstructive sleep apnea. One solutionpresented is stimulation of the hypoglossal nerve (CN XII) to activatemuscles that open the upper airway and/or maintain the stiffness of theairway to prevent collapse during sleep.

As shown in FIG. 1, the muscles that control the upper airway 28 and areinnervated by the hypoglossal nerve 29 include the geniohyoid muscle 30,the genioglossus muscle 32, the hyoglossus muscle 34 and thestyloglossus muscle 36. The genioglossus 32 is the main tongue protruder(the muscle that pushes the tongue out) and plays an important role inmaintaining the patency of the upper airway. For reference, FIG. 1 alsoshows the vagus nerve 50, the internal carotid artery 52, the intrinsicmuscles of the tongue 54 and the thyrohyoid muscle 56. Other structuresin the area, such as the ear, nose and mouth also are schematicallyillustrated and should be apparent.

Selective activation of one or more of the muscles in the upper airway28 can be effective in reducing the severity of sleep apnea andimproving airway patency. Moreover, selectively stimulating variousfascicles of the nerve can minimize the number of activated nervebranches while maximizing the therapeutic effectiveness of thestimulation. Fascicles of the hypoglossal nerve 29 can be individuallystimulated to activate functionally similar muscles (for example, thegenioglossus and geniohyoid muscles 32 and 42, which protrude the tongueand cause anterosuperior movement of the hyoid bone, respectively) toincrease the patency of the upper airway. In some cases, activatingfunctionally opposite muscles (for example, the genioglossus and thestyloglossus muscles 32 and 36), also has been found to be effective instiffening the airway to reduce the risk of collapse. This is probablyrelated to the fact that the tongue protruder muscles generally arestronger than the tongue retractor muscles. Thus, co-activation of thetongue protruder and retractor muscles can have a synergistic effectthat is advantageous during inspiration. While co-activation of thenerve branches innervating the tongue protruder and retractor musclescan be used during inspiration (as mentioned above) selective activationof the medial branch (innervating the genioglossus muscle 32) alone oras part of stimulating the entire nerve generally is effective forexpiration.

The threshold amplitude for muscle activation will vary from one patientto the next. To ensure an adequate response, the stimulation parametersare adjusted to stimulate at an amplitude of about 10% below thepatient's muscle activation threshold to about 20% over the patient'smuscle activation threshold. The amplitude of the electrical stimulationtypically is about 200 microamps (μA) to about 500 milliamps (mA). Othersuitable combinations of stimulation amplitude and frequency can beprovided on a patient-dependent basis. For example, the electricalstimulation can be provided by pulse trains of an intermittent durationor continuously, at a frequency of about 10 Hertz (Hz) to about 30 Hertz(Hz), with a pulse width of about 50 microseconds (μs).

In a first embodiment of the method, the electrical stimulation can beprovided to the hypoglossal nerve continuously throughout therespiration cycle, during both inspiration (breathing in) and expiration(breathing out) phases, to maintain the desired muscle tone for patencyof the upper airway. This is the simplest open-loop control system formaintaining the patency of the airway. Either the whole nerve isstimulated, or preferably one or more fascicles of the hypoglossal nerveare stimulated continuously to selectively activate the desired muscleor muscles. The stimulation has a relatively low amplitude, typicallyfrom about 10% below the patient's threshold amplitude up to thethreshold amplitude. In this method, the added stimulation can besufficient to activate the muscles on its own or can supplement andthereby amplify the electrical signals typically occurring in thehypoglossal nerve such that the combined amplitude is sufficient toactivate the muscles and thereby reduce the risk of collapse of thepatient's airway.

In a second embodiment of the method, the initiation of the electricalstimulation can be synchronized with a physical process, such asinspiration sensed by a remote sensor, without feedback from the nervebeing stimulated. Thus the system can include one or more sensors fordetecting a physical process, such as inspiratory efforts (i.e. thebeginning of an attempt to breathe), for example, other than through thesignals present in the hypoglossal nerve itself for activating themuscles. Various types of sensors are well known, including a pressuretransducer for monitoring the pressure in the upper airway, and sensorsthat detect movement of the chest wall. While this system does use inputfrom sensors to determine when to initiate a stimulation cycle, theinput is from a separate sensor and not feedback from the nerve beingstimulated, as is the case in a closed-loop system. In this system, noanalysis has to be made of the signal from the nerve being stimulated.

According to a variation of this method, the stimulation can be appliedto the lingual nerve in place of or in addition to stimulation appliedto the hypoglossal nerve. The lingual nerve is primarily a sensorynerve. The lingual nerve can be stimulated to induce the patient's brainto stimulate the hypoglossal nerve to increase the opening of theairway. In other words, stimulating the lingual nerve can induce areflex action that leads to activation of the hypoglossal nerve and themuscles innervated thereby rather than directly stimulating thehypoglossal nerve. As in the other variation described above, no sensingis conducted of the signals in the nerve being stimulated, which in thiscase is the lingual nerve.

In a third embodiment of the method, the controller can be programmed toprovide stimulation at a predetermined interval without either detectinga physical process or requiring feedback from the nerve beingstimulated. In this method, the stimulation interval can be determinedfrom the patient's nighttime basal metabolism, e.g., based on thepatient's observed nighttime resting respiratory rate. The resultanttiming of the stimulation pulse trains will closely simulate thepatient's normal nighttime respiration cycle. For example, a train ofstimulus pulses can be applied for about 2 seconds to about 3 seconds,and more particularly, for about 2½ seconds, with a wait of at least 2seconds to about 3 seconds between the pulse trains. The pulse trainscan each have an amplitude that is at or greater than the patient'sactivation threshold, up to about 20% above the patient's activationthreshold, for example. In this embodiment, the stimulation is providedat predetermined rate or pace without the added complexity ofclosed-loop feedback.

Other potential applications of this method, besides treatingobstructive sleep apnea (OSA), include supplemental nerve stimulation tokeep the airway open and treat snoring or for treating hypopnea, orcountering motor activation of the tongue during a seizure to preventthe tongue from protruding and being injured during the seizure, forexample. Other health problems related to the patency of a patient'sairway also can be treated using methods provided by the presentinvention.

Although the invention has been shown and described with respect tocertain illustrated embodiments, equivalent alterations andmodifications will occur to others skilled in the art upon reading andunderstanding the specification and the annexed drawings. In particularregard to the various functions performed by the above describedintegers (components, assemblies, devices, compositions, etc.), theterms (including a reference to a “means”) used to describe suchintegers are intended to correspond, unless otherwise indicated, to anyinteger which performs the specified function (i.e., that isfunctionally equivalent), even though not structurally equivalent to thedisclosed structure which performs the function in the hereinillustrated embodiments of the invention. In addition, while aparticular feature of the invention may have been described above withrespect to only one of several illustrated embodiments, such a featuremay be combined with one or more other features of the other embodiment,as maybe desired and advantageous for any given or particularapplication.

1. A method for treating sleep apnea, comprising: continuouslyelectrically stimulating at least one fascicle of a hypoglossal nerve ata predetermined amplitude of about 10% less than the threshold amplitudenecessary to activate a muscle of a patient up to 1% less than thethreshold amplitude necessary to activate a muscle of the patient.
 2. Amethod for treating sleep apnea, comprising: continuously electricallystimulating at least ten percent of the fascicles of the hypoglossalnerve with an electrical signal, where the electrical signal has anamplitude less than the threshold amplitude necessary to activate anupper airway dilator muscle of a patient, and where the electricalstimulus has an amplitude large enough so that a combination of theelectrical signal and an endogenous signal on the fascicles willactivate the upper airway dilator muscle.
 3. A method for treating sleepapnea, comprising: continuously electrically stimulating at least onefascicle that innervates the genioglossus at a predetermined amplitudeof about 10% less than the threshold amplitude necessary to activate afirst muscle of a patient up to 1% less than the threshold amplitudenecessary to activate the first muscle of the patient; and continuouslyelectrically stimulating at least one fascicle that innervates thestyloglossus nerve at a predetermined amplitude of about 10% less thanthe threshold amplitude necessary to activate a second muscle of apatient up to 1% less than the threshold amplitude necessary to activatethe second muscle of the patient, where the first muscle and the secondmuscle are functionally opposite muscles.